How to backup control file to trace on unix???

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#------------------------------------------------------------
# backup controlfile
#------------------------------------------------------------
#------------------------------------------------------------
# find the user_dump_dest directory through a sqlplus call
# and assign it to an environment variable
#------------------------------------------------------------
ORA_DUMP=`${ORACLE_HOME}/bin/sqlplus -s << EOF
/ as sysdba
set heading off
set feedback off
SELECT value
FROM v\\$parameter
WHERE name='user_dump_dest';
exit
EOF`
#------------------------------------------------------------
# create backup controlfile
#------------------------------------------------------------
${ORACLE_HOME}/bin/sqlplus -s <<> /dev/null 2>&1
/ as sysdba
set heading off
set feedback off
ALTER DATABASE BACKUP CONTROLFILE TO trace;
exit
EOF
#------------------------------------------------------------
# find the trace file that the backup controlfile is in
# this should be the last trace file generated
# validate it is a controlfile and copy to backup_control.sql
#------------------------------------------------------------
DATETIME="`date '+%d%m%y'`"
CONTROL=`ls -t $ORA_DUMP/*.trc | head -1`
if [ ! -z "$CONTROL" ]; then
grep 'CONTROL' ${CONTROL} 1> /dev/null
if test $? -eq 0; then
cp ${CONTROL} /home/oracle/backup_control_file_$DATETIME.sql
fi
fi
#end
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